1. Field of the Invention
This invention relates to a method of manufacturing a stay ring for a nongated turbine. More particularly, this invention relates to a method of manufacturing a stay ring for a family of nongated hydro-turbines where the stay ring is readily modified to permit selection of a desired power output for a particular turbine to be manufactured.
2. Description of the Prior Art
The power produced by a reaction turbine at a given rotational speed is proportional to the change in angular momentum of a mass of fluid flowing through the turbine runner. An angular momentum is imparted to the motive fluid by a spiral case and guide vanes. Prior art reaction turbines were provided with two sets of guidance--a stationary set (stay vanes) which provide structural support and an adjustable set (wicket gates) which permitted adjustment in the angular momentum of fluid flowing to the turbine runner. Accordingly, with adjustable wicket gates the power output of a reaction turbine could be regulated.
Currently, there is an emphasis to develop small, low head, low cost hydraulic installations. This emphasis is due in part to the rising costs of energy and the desirable low pollution levels attainable with hydraulic power production. Due to the economies of low head hydraulic power installations, regulated reaction turbines are commonly not economically feasible due in part to the high cost of designing and manufacturing wicket gates and their linkage and control mechanisms.
To utilize low head installations without the attendant high cost of regulated reaction turbines, stay rings, which previously had been used for structural support, were modified such that the stay vanes were shaped to impart a desired angular momentum to the motive fluid. In such nonregulated reaction turbines, a desired power output for the particular turbine was determined and a stay vane was formed to provide a desired discharge angle to meet the predetermined output level. In such cases, hydraulic turbine installations could be designed for low head installations which were set at a predetermined power output.
While the use of nonregulated reaction turbines as described above broadened the number of hydraulic sites which could be economically developed for power production, many other hydraulic sites are still not being developed since they are not cost effective even with the nongated reaction turbines. The lack of cost effectiveness for sites is due in part to the fact that the stay ring for the nongated reaction turbines must be individually designed for the particular site and the particular desired power output. A method of constructing a stay vane is shown in U.S. Pat. No. 4,135,853. The costs associated with the site-by-site design can frequently be sufficiently large that many hydraulic sites go undeveloped due to the lack of commercial effectiveness. To tap the energy associated with the undeveloped hydraulic sites and to lower the cost of nongated reaction turbines in general, a method is needed to standardize the design and construction of nongated reaction turbines while permitting modification of the design to accommodate different desired power outputs.